Fullerenes are a family of closed-caged molecules made up of carbon atoms. The closed-caged molecules consist of a series of five and six member carbon rings. The fullerene molecules can contain 500 or more carbon atoms. The most common fullerene is the spherical C60 molecule taking on the familiar shape of a soccer ball.
Fullerenes are typically produced by an arc discharge method using a carbon rod as one or both of the electrodes in a Krätschmer-Huffman generator. Krätschmer, W. et al., Chem. Phys. Lett., 170, 167-170 (1990) herein incorporated by reference in its entirety. Typically, the generator has a reaction chamber and two electrodes. The reaction chamber is evacuated and an inert gas is introduced in the reaction chamber at a controlled pressure. A potential is applied between the electrodes in the chamber to produce an arc discharge. The arc discharge forms a carbon plasma in which fullerenes of various sizes are produced.
Over the past decade, derivatives of the empty-cage C60 fullerene by organic functionalization chemistry has grown exponentially since the molecule was discovered to possess reactive double bonds at the [6,6] ring junctures of the cage, otherwise known as pyracyclene type units. Each C60 molecular cage contains six of these reactive units; however, the [6,6] junctures of larger empty cages like C70 and C78 are not as reactive as C60.
U.S. Pat. No. 6,303,760, herein incorporated by reference in its entirety, describes a family of endohedral metallofullerenes where a trimetallic nitride is encapsulated in a fullerene cage. The endohedral metallofullerenes have the general formula A3-nXnN@Cm (n=0-3) where A is a metal, X is a second trivalent metal, n is an integer from 0 to 3, and m is an even integer from about 60 to about 200. The metals A and X may be an element selected from the group consisting of a rare earth element and a group IIIB element and may be the same or different. In some embodiments, A and X may be selected from the group consisting of Scandium, Yttrium, Lanthanum, Gadolinium, Holmium, Erbium, Thulium, and Ytterbium, where A and X may be the same or different. These novel trimetallic nitride endohedral metallofullerenes are produced by introducing nitrogen gas into the Krätschmer-Huffman generator during vaporization of packed graphite rods containing corresponding metal oxides, known as the trimetallic nitride template (TNT) process.
Although novel derivatives of empty cages have been synthesized by organic functionalization chemistry, derivatives of endohedral metallofullerenes have not yet been produced. Derivatization of empty-cage fullerenes such as C60 occurs at highly reactive sites at a [6,6] ring junction of a pyracyclene-type units. These pyracyclene-type units are constructed of two fused hexagons abutted by neighboring pentagons. FIG. 1a illustrates the pyracyclene-type unit of a C60 fullerene cage. However, some larger fullerenes, such as C80, do not possess these reactive sites. Derivatives of endohedral metallofullerenes have the potential to provide the ability to create unique molecules with extraordinary properties due to the wide variety of metals and metal clusters that can be encapsulated inside the carbon cages of endohedral metallofullerenes. Accordingly, it is highly desirable to produce derivatives of these endohedral metallofullerenes.